Described on one website as "Marxist", the film has the potential to cause considerable consternation among the far-right party, which is highly critical of homosexuality.

In its manifesto for last week's local elections, the BNP said its councillors would "seek a local referendum asking parents for their backing for a local prohibition on the teaching of homosexuality as an alternative lifestyle choice".

However, Mr Barnbrook, a former teacher, denied the suggestion that HMS Discovery: A Love Story had a specifically gay focus, saying: "It's an art film, end of story.

"It was not a bloody porn film. The only nudity in it is a couple of guys running in a river. It is not about homosexuality. It is about sexuality.

"This was done when I was a student. It was part of my extra education, part of my studies and that was it. This was sometime back in the mid-80s."

The revelation has provoked glee among the BNP's opponents, however - particularly after the party's relative success in England's local elections, when it won 33 council seats and became the official opposition in Dagenham.